I have a problem with ActiveSync. Some users complains their callendars and contacts do not sync with Android 2.3. Email sync works on affected phones.
When I setup new phone, sync works fine both directions.
I found this error on our SBS 2011 ID 1040 - MSExchange ActiveSync, see attachment.
No 3rd party firewall on our server, just Windows firewall.
I did a server restart, did not help.